Hitherto, there is a block forming technique for block-forming (segmenting) an area of a document image. As such a block forming technique, there is a method of applying an image area separation (block selection) to image data of a document. According to such a method, the area of the document image is extracted by using a technique such as histogram, graph dividing method, or the like. As a technique using such a method, there is a technique disclosed in the Official Gazette of Japanese Patent Application Laid-Open No. H05-40849. In the Official Gazette of Japanese Patent Application Laid-Open No. H05-40849, first, the image data is scanned in the lateral direction and in the vertical direction and a histogram of a longest white run width is formed. An area extracting process is executed by using the formed histogram and an extracted area is classified into attributes of one of a field separator area, a photograph area, a graphics area, and another character area.
However, in the foregoing related art, it is a prerequisite that data serving as a target to be block-formed is an image. Therefore, in the case of applying the related art to, for example, a structured document, it is necessary to temporarily rasterize drawing data in the structured document and to further perform the image area separation by using the technique such as histogram or graph division. There is, consequently, such a problem that it takes a long time until the block formation (extraction of the area) is completed.
The invention is made in consideration of such a problem and it is an object of the invention to enable an area of a document image to be block-formed at a speed higher than that in the related art.